Biao Zhang,Feng Ye,Ye Gao,Qiang Liu,ShiChao Liu,Limeng Liu
Bisphenol-A cyanate ester resin (BADCy)/Ni 0.5 Ti 0.5 NbO 4 composites with novel structure, within which Ni 0.5 Ti 0.5 NbO 4 and BADCy are continuous directional distribution and parallel to the electric field direction (marked as composite-directional), were designed and fabricated using freeze casting combined with vacuum assisted infiltration process. Dielectric properties as well as the moisture absorption of the composites were studied. Theoretical models used to predict the dielectric properties of the composites were established. Results show that the novel structure can significantly improve the dielectric constant while decrease dielectric loss compare with traditional structure in which Ni 0.5 Ti 0.5 NbO 4 filler is homogeneously distributed (the composite marked as composite-homogeneous). Dielectric constant of composite-directional is as high as 19.93 while dielectric loss is only 4.07 × 10 −3 (at 7319 MHz) when Ni 0.5 Ti 0.5 NbO 4 content is 43.79 vol%. Furthermore, the dielectric constant of both composite-directional and composite-homogeneous can be predicted using Rother-Lichtenecker model when the fitting parameters ( n ) are −0.5188 and −0.1499, respectively. Distribution state of Ni 0.5 Ti 0.5 NbO 4 is the main reason for the difference of fitting parameters. Due to the excellent properties of composite-directional, this kind of composites can be used as printed circuit board (PCB) materials.
Hyperbranched fluorine and epoxy containing PBO precursor (epoxy- pre FHBPBO) was synthesized and utilized as interface compatibilizer to synchronously improve the mechanical and dielectric properties of poly( p -phenylene-2, 6-benzobisoxazole) (PBO) fibres reinforced bisphenol A dicyanate ester (BADCy) resins (PBO fibres/FHBPBO- co -BADCy) laminated composites. 1 H NMR, 13 C NMR, and FTIR analyses confirmed the successful preparation of epoxy- pre FHBPBO. The introduction of hyperbranched structure and fluorine groups significantly improved the mechanical properties and wave-transparent performance. Compared with PBO fibres/BADCy, the flexural strength and interlaminar shear strength of PBO fibres/FHBPBO- co -BADCy composites with 7 wt% epoxy- pre FHBPBO were respectively enhanced to 634.9 and 46.9 MPa, increased by 8.1% and 27.8%. The corresponding dielectric constant and dielectric loss were 2.65 and 0.003, respectively, lower than those of PBO fibres/BADCy (3.06 and 0.006) composites. Meanwhile, the corresponding volume resistivity and breakdown strength were 4.93 × 10 15 Ω•cm and 25.38 kV/mm, higher than PBO fibres/BADCy resins composites (2.2 × 10 15 Ω•cm and 17.69 kV/mm).
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